Facts about bird flu

Facts about bird flu

Key questions and answers at a glance

Bird flu, avian flu, avian influenza ... what’s what?

What do H and N stand for in virus names?

How do the viruses spread?

How dangerous is bird flu for humans?

When is there a risk of a pandemic?

What precautions should be taken when travelling?

Further information

Bird flu, avian flu, avian influenza ... what’s what?

The three names refer to the same disease or, to be more accurate, the same group of diseases: the bird flu does not exist.

Bird flu is caused by the type A influenza viruses. The viruses occur naturally in wild birds, primarily aquatic birds, and usually in the gastrointestinal tract but also in the airways. The infected birds rarely contract the disease themselves or only very mildly. The viruses arise in the form of low-pathogenic avian influenza (NPAI).

It is assumed that these viruses, which are not very infectious, can be transmitted to poultry and can then mutate into highly pathogenic avian influenza (HPAI) as a result of close contact between the individual virus strains. If these viruses are transmitted back to wild birds they can then be spread through avian migration. In such cases, a lot of the wild birds die of the disease, but far from all of those infected with the virus.

What do H and N stand for in virus names

Influenza A viruses are named after their structure and divided into subtypes. They differ in terms of their surface proteins: H stands for haemagglutinin proteins and N for neuraminidase proteins.

Sixteen different H subtypes and nine different N subtypes are known and can combine to form numerous different  viruses:

    H1, H2, H3 are the pathogens responsible for human influenza.

   The subtypes H5 and H7 cause the bird flu, which mainly affects poultry.

    Wild birds are a natural reservoir for all of these influenza viruses.

Some types of influenza A viruses are species-specific and arise, for example, in pigs, whales, horses, seals and humans.

How do the viruses spread?

Avian influenza A viruses are mainly excreted in the faeces of infected birds and can maintain their pathogenicity for long periods in water and mud. They infect the next animal via the oral and nasal cavities, settle in the mucous membranes and continue to reproduce there.

In practice, this means that viruses are introduced into the water with the faeces and then taken in by other individuals. Moreover, infection via the inhalation of infected dust and droplets is also possible.

Influenza A viruses usually circulate within one and the same species, but they can also cross species boundaries and be transmitted, for example, from humans to pigs or, in the case of bird flu, from wild birds to poultry. Transmission can also arise in the opposite direction.

How dangerous is bird flu for humans?

The H5N8 subtype, which is currently circulating in Germany, has already been detected in previous outbreaks all over the world. Humans have never been affected by it. The possibility of transmission to humans, however, cannot be excluded with absolute certainty.

In contrast, the influenza A virus H5N1 can cause severe illness and pneumonia in humans. It originates from infected poultry and can be transmitted in individual cases to humans who come into close contact with infected birds.

 Particular caution is advised in the following cases:

Where direct contact arises between birds and humans, e.g. in poultry plants and in the handling of dead birds.

In the handling of intermediate hosts, e.g. pigs. All previous cases involving infection with the H5N1 virus involved very close contact with poultry or pigs. The infection of “non participants”, e.g. people who spend time in the vicinity of poultry farms, has not yet been reported.

In the consumption of poultry and eggs.

Even if transmission via food is highly unlikely, during a H5N1 outbreak, food should be heated to over 70 degrees for at least five minutes.

When is there a risk of a pandemic?

When two influenza viruses that originate in different species, e.g. pigs and humans, meet in an organism, genetic information from the two viruses can mix to form a new virus. This can also occur through the continuous mutation of a virus.

Such a virus, with its new surface characteristics, would then encounter an immune system that is either entirely unprepared for it or only capable of offering a completely inadequate immune response. If the new virus triggers disease symptoms and can easily be transmitted between humans, for example through hand-shaking or sneezing, the risk of a pandemic arises, whereby vast numbers of people throughout the world would develop the disease within a very short period of time.

Because scientists cannot predict the characteristics of such new viruses, it is not possible to develop specific vaccines against them. It is equally impossible to predict where such mixtures of viruses could arise.

The fact that the human influenza virus H3N2 also arises in pigs in south China, one of the main areas for outbreaks of the highly infectious H5N1 subtype, has been a source of concern for a long time. It means that there is a far greater risk that these two viruses will meet here and their DNA will combine to form a dangerous new virus.

What precautions should be taken when travelling?

People travelling in countries in which H5N1 arises should inform themselves about the current situation there in advance, e.g. through the websites of the Federal Foreign Office, WHO, the Robert Koch Institute and the Friedrich-Löffler-Institut (Federal Research Institute for Animal Health).

In general, contact with poultry and pigs at markets or farms should be avoided and regular hand washing is essential.

In addition to this, when travelling to affected regions, it is important to carry disinfectants, thermometers and, if appropriate, antiviral drugs.

If you develop symptoms associated with a suspected bird flu infection, you must consult a doctor immediately and contact the embassy.

Supplementary insurance covering eventual transport home in the event of illness may be useful.

On return from travel in an affected area, it is important to check your temperature and keep an eye out for possible symptoms for ten days. Consult a doctor immediately in the case of suspected infection.

The import of birds, feathers and eggs is strictly prohibited.

Further information

Friedrich-Löffler-Institut (FLI)

Other Interesting Articles

Go to Editor View